U.S. patent number 8,617,422 [Application Number 12/568,063] was granted by the patent office on 2013-12-31 for use of codoping to modify the scintillation properties of inorganic scintillators doped with trivalent activators.
This patent grant is currently assigned to Siemens Medical Solutions USA, Inc., University of Tennessee Research Foundation. The grantee listed for this patent is Lars A. Erikkson, Merry Anna Koschan, Charles L. Melcher, Harold E. Rothfuss. Invention is credited to Lars A. Erikkson, Merry Anna Koschan, Charles L. Melcher, Harold E. Rothfuss.
United States Patent |
8,617,422 |
Koschan , et al. |
December 31, 2013 |
Use of codoping to modify the scintillation properties of inorganic
scintillators doped with trivalent activators
Abstract
Crystals with improved scintillation and optical properties are
achieved by codoping with a trivalent dopant and a divalent and/or
a monovalent dopant. Embodiments include codoping LSO, YSO, GSO
crystals and LYSO, LGSO, and LYGSO crystals. Embodiments also
include codoped crystals with a controlled monovalent or
divalent:trivalent dopant ratio of from about 1:1 for increased
light yield to about 4:1 for faster decay time.
Inventors: |
Koschan; Merry Anna (Maryville,
TN), Melcher; Charles L. (Oak Ridge, TN), Erikkson; Lars
A. (Oak Ridge, TN), Rothfuss; Harold E. (Knoxville,
TN) |
Applicant: |
Name |
City |
State |
Country |
Type |
Koschan; Merry Anna
Melcher; Charles L.
Erikkson; Lars A.
Rothfuss; Harold E. |
Maryville
Oak Ridge
Oak Ridge
Knoxville |
TN
TN
TN
TN |
US
US
US
US |
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Assignee: |
Siemens Medical Solutions USA,
Inc. (Malvern, PA)
University of Tennessee Research Foundation (Knoxville,
TN)
|
Family
ID: |
42056385 |
Appl.
No.: |
12/568,063 |
Filed: |
September 28, 2009 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20100078595 A1 |
Apr 1, 2010 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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61100332 |
Sep 26, 2008 |
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Current U.S.
Class: |
252/301.4F |
Current CPC
Class: |
C30B
15/00 (20130101); C09K 11/7774 (20130101); C30B
29/34 (20130101) |
Current International
Class: |
C09K
11/02 (20060101) |
Field of
Search: |
;252/301.4F,301.6R,301.17 ;250/370.11,483.1 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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WO 2005028590 |
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Mar 2005 |
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WO |
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Other References
Spurrier et al. `The effect of co-doping on growth stability and
scintillation properties of lutetium oxyorthosilicate`, Nov. 6,
2007, Journal of Crystal Growth 310, pp. 2110-2114. cited by
examiner .
Zavartsev et al. Czochralski growth and characterisation of large
Ce3+:Lu2SiO5 single crystals co-doped with Mg2+ or Ca2+ or Tb3+ for
scintillators, Jan. 1, 2005, Journal of Crystal Growth 275, pp.
2167-2171. cited by examiner .
Jacquemet, M., et al., "Efficient laser action of Yb:LSO and Yb:YSO
oxyorthosilicates crystals under high-power diode-pumping", Applied
Physics B 80, 171-176 (2005). cited by applicant .
Rothfuss, et al., "The Effect of Ca2+ Codoping on Shallow Traps in
YSO:Ce Scintillators", IEEE Transactions on Nuclear Science, Vol.
56, No. 3, Jun. 2009. cited by applicant .
Rothfuss, et al., "Codoping YSO: Ce with Calcium to Improve
Fundamental Properties", University of Tennessee. cited by
applicant .
Yang, et al "The effect of calcium co-doping on praseodymium doped
LSO", 2008 Symposium on Radiation Measurements and Applications,
Jun. 2-5, 2008, Berkeley, California, USA. cited by applicant .
Spurrier, et al., "The effect of co-doping on the gowth stability
and scintillaton properties of lutetium oxyorthosilicate",
ScienceDirect, Journal of Crystal Growth 310 (2008) 2110-2114.
cited by applicant .
Spurrier, et al., "Effects of Ca2+ Co-Doping on the Scintillation
Properties of LSO:Ce", IEEE Transactions on Nuclear Science, vol.
55, No. 3, Jun. 2008. cited by applicant .
Thibault, et al, Efficient diode-pumped Yb3+: Y2SiO5 and
Yb3+:Lu2SiO5 high-power femtosecond laser operation, Optics
Letters, May 15, 2006/vol. 31, No. 10. cited by applicant .
Yang, et al., The Effect of Calcium Co-Doping on Praseodymium Doped
LSO, IEEE Transactions on Nuclear Science, vol. 56, No. 3, Jun.
2009. cited by applicant .
Zavartsev, et al., "Czochralski Growth and Characterisation of
Large Ce3+:Lu2SiO5 Single Crystals Co-doped with Mg2+ or Ca2+ or
Tb3+ for Scintillators", Journal of Crystal Growth 275 (2005)
e2167-e2171. cited by applicant.
|
Primary Examiner: Le; Emily
Assistant Examiner: Edmondson; Lynne
Attorney, Agent or Firm: Kendall; Peter
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS AND CLAIM FOR PRIORITY
This application is a non-provisional of, and claims priority under
35 U.S.C. .sctn.119(e) from, provisional application Ser. No.
61/100,332, filed Sep. 26, 2008, entitled Use Of Codoping To Modify
The Scintillation Properties Of Inorganic Scintillators Doped With
Trivalent Activators, and provisional application Ser. No.
61/100,328, filed Sep. 26, 2008, entitled Codoping YSO:Ce With
Calcium To Improve Fundamental Properties. This application is also
a continuation-in-part of U.S. patent application Ser. No.
11/842,813, entitled Lutetium Oxyorthosilicate Scintillator Having
Improved Scintillation and Optical Properties and Method of Making
the Same, filed on Aug. 21, 2007, the entire disclosure of which is
incorporated herein by reference into the present application.
Claims
What is claimed is:
1. A scintillation material, comprising a crystal consisting
essentially of:
T.sub.2xLu.sub.2(1-x-y-z)Y.sub.2yGd.sub.2zSiO.sub.5; and at least
one divalent codopant, wherein T is a trivalent activator dopant
selected from the group consisting of Pr, Eu, Er and Yb,
0<2x<0.2, 0.ltoreq.2y.ltoreq.2(1-x),
0.ltoreq.2z.ltoreq.2(1-x), and 0.ltoreq.(y+z).ltoreq.(1-x), wherein
the ratio (a):(b) of the divalent dopant concentration (a) to the
trivalent activator dopant concentration (b) is about 1:1, to
maximize light output.
2. The scintillation material according to claim 1, wherein
0.ltoreq.(y+z)<(1-x), such that the crystal includes Lu.
3. The scintillation material according to claim 1, wherein the
divalent codopant comprises Mg, Ca, Ba, Zn, or Cu.
4. The scintillation material according to claim 3, wherein the
trivalent activator dopant consists of Pr and the codopant
comprises Ca.
5. A medical imaging device comprising the scintillation material
according to claim 1.
6. A positron emission tomography (PET) scanner comprising the
scintillation material according to claim 1.
7. A laser device comprising the scintillation material according
to claim 1.
8. An oil exploration device comprising the scintillation material
according to claim 1.
9. An optical data storage device comprising the scintillation
material according to claim 1.
10. A scintillation detector comprising the scintillation material
according to claim 1.
11. A method comprising detecting gamma rays, X-rays, cosmic rays,
and particles having an energy of 1 keV or greater using the
scintillation detector according to claim 10.
12. A scintillator material comprising a ceramic comprising:
T.sub.2xLu.sub.2(1-x-y-z)Y.sub.2yGd.sub.2zSiO.sub.5; and at least
one monovalent and/or divalent codopant, wherein T comprises at
least one trivalent activator dopant, 0<2x<0.2,
0.ltoreq.2y.ltoreq.2(1-x), 0.ltoreq.2z.ltoreq.2(1-x), and
0.ltoreq.(y+z).ltoreq..ltoreq.(1-x).
13. A method comprising growing a crystal consisting essentially
of: T.sub.2xLu.sub.2(1-x-y-z)Y.sub.2yGd.sub.2zSiO.sub.5; and at
least one monovalent and/or divalent codopant, wherein T is a
trivalent dopant selected from the group consisting of Pr, Eu, Er
and Yb, 0<2x<0.2, 0.ltoreq.2y.ltoreq.2(1-x),
0.ltoreq.2z.ltoreq.2(1-x), and 0.ltoreq.(y+z).ltoreq.(1-x), the
method further comprising controlling the ratio (a):(b) of the
divalent dopant concentration (a) to the trivalent activator dopant
concentration (b) to about 1:1 when the codopant is divalent.
14. A scintillation material, comprising a crystal consisting
essentially: T.sub.2xLu.sub.2(1-x-y-z)Y.sub.2yGd.sub.2zSiO.sub.5;
and at least one divalent codopant, wherein T is a trivalent
activator dopant selected from the group consisting of Pr, Eu, Er
and Yb, 0<2x<0.2, and 0<2(y+z).ltoreq.2(1-x), wherein the
ratio (a):(b) of the divalent dopant concentration (a) to the
trivalent activator dopant concentration (b) is about 1:1, to
maximize light output.
15. The scintillation material of claim 14, wherein x+y+z is
substantially 1.
Description
TECHNICAL FIELD
The present disclosure relates to crystal materials with improved
scintillation and optical characteristics. The present disclosure
is applicable to inorganic scintillation crystal materials, such as
oxyorthosilicates (Ln.sub.2SiO.sub.5) where Ln is Lutetium (Lu),
Yttrium (Y), and/or Gadolinium (Gd), i.e., LSO, YSO, GSO, LYSO,
LGSO, and (LYGSO.
BACKGROUND
Scintillation detectors are used in a wide variety of applications,
including medical diagnostics and therapy (PET, SPECT, therapy
imaging, etc.), oil exploration, field spectrometry, and container
and baggage scanning. Desirable properties for scintillation
detectors include high light output (i.e., a high efficiency for
converting the energy of incident radiation into scintillation
photons), efficient detection of the radiation being studied, a
high stopping power, good linearity over a wide range of energy, a
short rise time for fast timing applications, and a short decay
time to reduce detector dead-time and accommodate high event rates.
Light output is particularly important, as it affects both the
efficiency and resolution of the detector, where efficiency is the
ratio of detected particles to the total number of particles
impinging upon the detector, and energy resolution is the ratio of
the full width at half maximum of a given energy peak to the peak
position, usually expressed in percent. The light output is often
quantified as a number of scintillation photons produced per MeV of
deposited energy.
LSO is a scintillation crystal that is widely used in medical
imaging applications, such as for gamma-ray detection in Positron
Emission Tomography (PET). LSO is typically doped with 0.05 to 0.5%
cerium (Ce), while controlling other impurities at low levels. The
light yield of Ce doped LSO (Ce:LSO) crystals grown using prior art
methods is on average significantly lower than the theoretical
maximum, and the decay time of these crystals tends to be in the 40
ns range. In addition, new techniques for image data acquisition
require faster decay times than those obtained with Ce:LSO.
Further, scintillation properties of LSO grown under such
conditions can vary significantly from boule to boule, and in
different parts of the same boule, which consequently increases the
cost of commercial crystal production caused by the large number of
out-of-spec crystals produced.
Work has been done with codoping the LSO crystals in an attempt to
improve the scintillation properties. For example, Ce:LSO has been
doped with 0.02% calcium (Ca) or magnesium (Mg). However, although
codoping improved light yield some, it failed to change decay time
for the crystals.
A need therefore exists for scintillation crystals with improved
light yield and light yield uniformity, controllable scintillation
decay time that can be optimized for specific applications, and
improved decay time uniformity. A need also exists for production
techniques with improved yield by reducing the number of
out-of-spec crystals produced.
SUMMARY
An aspect of the present disclosure is a crystal exhibiting
increased light output and reduced decay times.
Additional aspects and other features of the present disclosure
will be set forth in the description which follows and in part will
be apparent to those having ordinary skill in the art upon
examination of the following or may be learned from the practice of
the present disclosure. The advantages of the present disclosure
may be realized and obtained as particularly pointed out in the
appended claims.
According to the present disclosure, some technical effects may be
achieved in part by a crystal comprising:
T.sub.2xLu.sub.2(1-x-y-z)Y.sub.2yGd.sub.2zSiO.sub.5 and at least
one monovalent and/or divalent codopant, wherein T comprises at
least one trivalent dopant, 0<2x<0.2,
0.ltoreq.2y.ltoreq.2(1-x), 0.ltoreq.2z.ltoreq.2(1-x), and
0.ltoreq.(y+z).ltoreq.(1-x).
Aspects include a crystal having a ratio (a):(b) of the divalent
dopant concentration (a) to a trivalent dopant concentration (b) of
about 1:20 to about 20:1, for example about 1:1, to maximize light
output, or about 4:1 to about 6:1, e.g., about 4:1 to about 5:1, to
minimize decay times. The concentrations are with respect to
initial starting raw materials; due to varying segregation
coefficients in melt grown crystals the ratio in the finished
crystals could differ. A further aspect includes crystals doped
with a trivalent activator comprising Ce, Pr, Eu. Er, or Yb, e.g.
Ce. Another aspect includes crystals codoped with Na, K, Mg, Ca,
Ba, Zn, or Cu, e.g. Ca. Other aspects include a medical imaging
device such as a positron emission tomography scanner, a laser
device, an oil exploration device, an optical data storage device,
or a scintillation detector, and use thereof, comprising the
codoped crystal.
Additional aspects and technical effects of the present disclosure
will become readily apparent to those skilled in the art from the
following detailed description wherein embodiments of the present
disclosure are described simply by way of illustration of the best
mode contemplated to carry out the present disclosure. As will be
realized, the present disclosure is capable of other and different
embodiments, and its several details are capable of modifications
in various obvious respects, all without departing from the present
disclosure. Accordingly, the drawings and description are to be
regarded as illustrative in nature, and not as restrictive.
BRIEF DESCRIPTION OF THE DRAWINGS
The present disclosure is illustrated by way of example, and not by
way of limitation, in the figures of the accompanying drawing and
in which like reference numerals refer to similar elements and in
which:
FIG. 1 graphically illustrates light yield for a Ce:LSO crystal as
a function of Ca.sup.2+ concentration;
FIG. 2 graphically illustrates decay time measurements for Ca doped
Ce:LSO crystals;
FIG. 3 shows how the decay constant decreases monotonically with
increasing Ca concentration;
FIGS. 4A and 4B graphically illustrate the decay time for Ce:YSO
without codoping and with 0.1% Ca codoping, respectively;
FIG. 5 graphically illustrates decay times for Ca doped Ce:LSO and
Ce:YSO; and
FIGS. 6A and 6B graphically illustrate decay time of Pr:LSO without
codoping and with Ca in a 1:1 ratio to Pr, respectively.
DETAILED DESCRIPTION
In the following description, for the purposes of explanation,
numerous specific details are set forth in order to provide a
thorough understanding of exemplary embodiments. It should be
apparent, however, that exemplary embodiments may be practiced
without these specific details or with an equivalent arrangement.
In other instances, well-known structures and devices are shown in
block diagram form in order to avoid unnecessarily obscuring
exemplary embodiments.
The present disclosure addresses the issues of low light output and
slow decay time in a scintillation crystal. In accordance with
embodiments of the present disclosure, a crystal is doped with both
a trivalent dopant and a monovalent and/or divalent codopant. By
controlling the ratio (a):(b) of the codopant concentration (a) to
the trivalent dopant concentration (b) for a particular situation,
the light yield and decay times can be improved and optimized. In
addition, the use of the codopant improves production yield.
Embodiments of the present disclosure include a crystal with the
chemical formula
T.sub.2xLu.sub.2(1-x-y-z)Y.sub.2yGd.sub.2zSiO.sub.5 and at least
one monovalent and/or divalent codopant, wherein T comprises at
least one trivalent dopant, 0<2x<0.2,
0.ltoreq.2y.ltoreq.2(1-x), 0.ltoreq.2z.ltoreq.2(1-x), and
0.ltoreq.(y+z).ltoreq.(1-x). The trivalent dopant comprises, for
example, Ce, Pr, Eu, Er, or Yb, and the monovalent and/or divalent
codopant(s) comprise, for example, Na, K, Mg, Ca, Ba, Zn, or Cu.
The concentrations of the codopant (a) and the trivalent dopant (b)
are controlled such that a ratio of (a):(b) ranges from about 1:20
to about 20:1. For higher light output the ratio (a):(b) may be
about 1:1, whereas for shorter decay times, the ratio (a):(b) may
be about 4:1 to about 6:1, for example about 4:1 to about 5:1. The
concentrations are with respect to initial starting raw materials;
due to varying segregation coefficients in melt grown crystals the
ratio in the finished crystals could differ. The crystal may be a
part of a medical imaging device, such as a positron emission
tomography (PET) scanner, a laser device, an oil exploration
device, or an optical data storage device.
Still other aspects, features, and technical effects will be
readily apparent to those skilled in this art from the following
detailed description, wherein preferred embodiments are shown and
described, simply by way of illustration of the best mode
contemplated. The disclosure is capable of other and different
embodiments, and its several details are capable of modifications
in various obvious respects. Accordingly, the drawings and
description are to be regarded as illustrative in nature, and not
as restrictive.
Crystals according to exemplary embodiments of the disclosure may
be grown by the Czochralski method. However, single crystals or
polycrystalline materials or ceramics grown or produced by other
methods may also be employed.
FIG. 1 graphically illustrates light yield for a Ce:LSO crystal as
a function of Ca.sup.2+ concentration. The amount of Ce in each
sample was 0.1 atomic (at.) % (where at. % refers to the
concentration in starting raw materials with respect to lutetium
(Lu)). The Ca doped crystals had up to 25% more light output when
compared to the high quality Ce-only reference crystal. The best
light yield was obtained for 0.1% Ca with the light yield
decreasing gradually for crystals with higher Ca concentrations.
The error bars represent the standard deviation of the individual
samples within a boule. Repeatability of measurements on a single
sample is about 3%.
Decay time measurements for the Ca doped crystals are graphically
illustrated in FIG. 2. The decay of each crystal can be
characterized by a single exponential decay, although it is clear
that the Ca doped crystals have significantly faster decay compared
to LSO doped only with Ce. FIG. 3 shows how the decay constant
decreases monotonically with increasing Ca concentration. Each
point represents the average of multiple samples from a boule with
a given Ca concentration. The error bars represent the standard
deviation (about 1 ns) of the individual samples within a boule.
Repeatability of measurements on a single sample is about 0.5 ns.
Crystals with about 0.3 to about 0.4% Ca have the fastest decay
time of about 31 ns compared to 43 ns for LSO doped only with
Ce.
The relationship between decay time and light yield for Ca doped
crystals is illustrated in Table 1. Light output and decay time
values in Table 1 represent the average of multiple samples.
TABLE-US-00001 TABLE 1 PROPERTIES OF LSO:CE,CA CRYSTALS Light
output Ca concentration (%) (photons/MeV) Decay time (ns) 0.0 30900
43.0 0.1 38800 36.7 0.2 36200 33.3 0.3 32400 31.3 0.4 34800
31.0
A correlation is apparent in which the decay time becomes faster
with decreasing light yield. The Ca doped crystals with the fastest
decay time (31 ns) have light output higher than that of the
reference crystal that has a decay time of 43 ns.
In the above example, the concentration of Ce in the samples was
0.1%, and the ratio of Ca to Ce (excluding the reference sample)
ranged from about 1:1 to about 4:1. The amount of Ce may range
widely, for example from about 0.01 to about 1%. As evident from
Table 1, any concentration of Ca raised the light output and
decreased the decay time relative to the reference crystal with no
Ca. Accordingly, embodiments of the disclosure include amounts of
Ca greater than 0%. However, the light output peaked at about a 1:1
ratio of Ca to Ce and the decay time was fastest around a 4:1
ratio. It has been found that it is not the absolute concentration
of Ca, but rather the ratio of Ca to Ce that determines the decay
time and light yield. The ratio of Ca to Ce should range from about
1:20 to about 20:1, for improved light output and decay time, but
for example about 1:1 for highest light output or about 4:1 to
about 6:1, such as 4:1 to about 5:1, for fastest decay times. The
concentrations are with respect to initial starting raw materials:
due to varying segregation coefficients in melt grown crystals the
ratio in the finished crystals could differ. By manipulating the
relative concentrations of Ca and Ce, it is possible to pre-select
the decay time of the finished crystals within a range of about 28
to about 43 ns, with the shortest decay times being achieved by the
highest ratio.
Although Table 1 shows the relationship between Cu concentration,
decay time, and light yield, additional or other divalent and/or
monovalent co-dopants may also be used, for example sodium (Na),
potassium (K), magnesium (Mg), barium (Ba), zinc (Zn), or copper
(Cu), and other similar elements.
The focus has been on Ce:LSO. However, YSO (Y.sub.2SiO.sub.5), and,
GSO (Gd.sub.2SiO.sub.5) are both similar in structure and
properties to LSO. In actuality, the crystal may be characterized
by the formula T.sub.2xLu.sub.2(1-x-y-z)Y.sub.2yGd.sub.2zSiO.sub.5
and at least one monovalent and/or divalent codopant, wherein T
comprises at least one trivalent dopant, 0<2x<0.2,
0.ltoreq.2y.ltoreq.2(1-x), 0.ltoreq.2z.ltoreq.2(1-x), and
0.ltoreq.(y+z).ltoreq.(1-x). While there are some fundamental
variations in properties, such as density, thermal response,
scintillation light yield, and decay time, that may make one type
of crystal more suitable than another for specific applications,
they are sufficiently similar to consider them to be substantially
interchangeable.
For example, Ce doped YSO was grown both with and without Ca. The
concentration of Ce was 0.1 at. % in each sample, and the
concentration of Cu was 0.1 at. % in one sample (i.e., a 1:1 ratio
of Co to Ce), and none in another sample. From initial studies of
the Ce:YSO crystals, it was found that the electron traps play a
significant role by increasing the decay time and adding additional
decay time components in the decay scheme. This effect was observed
by measuring the decay scheme using a Bollinger-Thomas setup at
room temperature and comparing it to the same measurement taken at
40K. The measurement seen at 40K showed that when the charge traps
become saturated, the trap lifetimes are on the order of years and
become insignificant in the decay scheme. This effect results in a
shorter decay time and fewer decay time components in the decay
time profile. FIGS. 4A and 4B graphically illustrate the decay time
for Ce:YSO without codoping and with 0.1% Ca codoping,
respectively. As shown, the decay time dropped for the sample with
Ca (with a 1:1 Ca:Ce, ratio).
FIG. 5 shows decay times for different Ca:Ce ratios for both LSO
and YSO. With the understanding that YSO normally has a longer
decay time than LSO, it can be seen from FIG. 5 that YSO and LSO
both respond similarly to codoping with varying Ca:Ce ratios even
for different values of Ce.
Although Ce:LSO is commonly used in medical imaging, codoped
Ce:YSO, Ce:GSO, Ce:LYSO, and Ce:LGSO may also be used in the
medical imaging field. There are also non-medical imaging
applications for these crystals. For example, Ce:GSO which is
particularly useful in oil exploration may be codoped to improve
the detector characteristics.
The disclosure also is not limited to Ce as the activator. Other
non-cerium trivalent dopants, such as praseodymium (Pr), europium
(Eu), erbium (Er), and/or Ytterbium (Yb) may be incorporated into
the scintillators. For example, in accordance with another
exemplary embodiment, LSO was grown doped with 0.2 atomic % Pr as
an activator. One sample of the Pr:LSO was codoped with 0.2 atomic
% Ca, and a second sample was not codoped. The Pr:LSO that was
codoped, with about a 1:1 ratio of Ca to Pr, had an intensified
color relative to the other sample with an accompanying change in
absorbance spectra. Pr:YSO, Eu:YSO, Er:YSO, Nd:YSO, and Yb:YSO,
which are similar in structure to Pr:LSO, are also used for lasers.
These crystals may be codoped to modify the optical properties.
Pr:YSO and other variants may also be used for applications such as
optical data storage.
Calcium codoping also has an impact on the decay time of Pr:LSO, as
shown in FIGS. 6A (not codoped) and 6B (codoped with Ca in a 1:1
ratio to Pr). The Ca codoping favors the fast component of
scintillation decay, making it desirable for medical imaging. In
addition, the emission spectra are modified by calcium, which
appears to act as an absorber (or internal filter) for short
wavelength emissions.
In addition to improving light yield and reducing decay time,
codoping with monovalent and/or divalent dopants further increases
the average quality of the crystals produced. Fewer crystals are
grown that are out of spec. Thus, codoping with Ca, for example, is
cost effective, as a higher percentage of the crystals that are
grown can be used.
The embodiments of the present disclosure can achieve several
technical effects, including reduced decay times, improved light
yield, modified optical properties, and greater uniformity in the
production of crystals. The present disclosure enjoys industrial
applicability in medical imaging, oil exploration, optical data
storage, lasers, and homeland security.
In the preceding description, the present disclosure is described
with reference to specifically exemplary embodiments thereof. It
will, however, be evident that various modifications and changes
may be made thereto without departing from the broader spirit and
scope of the present disclosure, as set forth in the claims. The
specification and drawings are, accordingly, to be regarded as
illustrative and not as restrictive. It is understood that the
present disclosure is capable of using various other combinations
and embodiments and is capable of any changes or modifications
within the scope of the inventive concept as expressed herein.
* * * * *